With the development of optical communication, an optical transceiver module is used more and more widely in optical fiber communication systems. The optical transceiver module is a key technology of optical fiber communication systems and plays the role of realizing electrical to optical and optical to electrical conversion, thus its performance has a significant impact on that of optical fiber communication systems. An optical transceiver module usually employs an Electro-absorption Modulated Laser (EML); the EML mainly includes: a Photo-detector (PD), a Laser Diode (LD) and an Electro-absorption Modulator (EAM); the PD is used for converting an optical signal into an electrical signal; the LD is used for generating laser; in order to enable the LD to generate laser, a bias current must be injected into it, which means the bias current flows from anode to cathode of the LD; the EAM utilizes the laser generated by the LD as an optical carrier wave, modulates the optical carrier wave with a modulation voltage, and generates a modulated optical signal. The principle that the EAM modulates the laser generated by the LD is as follows: the EAM is added with an appropriate reverse bias voltage, and because of the nonlinear absorption property of the EAM, in the range of modulation of EAM, the absorption of light intensity of the EAM increases in an approximately exponential manner with an increase in the reverse bias voltage, so that only a very low optical power transmits when the reverse bias voltage increases. Thus, after being modulated by the EAM, the optical carrier wave output carries a modulation voltage signal.
In the traditional EML, there are two coupling modes between a driver for providing the modulation voltage and the EAM; one coupling mode is the traditional Direct Current (DC) coupling mode; as shown in FIG. 1, output of the driver is directly connected to the anode of EAM, and the cathode of the EAM is grounded; R1 is a matching resistor and connected to two ends of the EAM. However, the driver and the EAM use a DC coupling mode; in order to achieve good indexes of high extinction ratio and dispersion cost, the amplitude of the alternate current signal output by the driver is required to be large enough, so the required power consumption of the driver is high, which causes the high power consumption of the EML.
The other coupling mode is the traditional Alternate Current (AC) coupling mode; as shown in FIG. 2, output of the driver is connected to the anode of EAM via the capacitor C1, and the cathode of the EAM is grounded; because of using the AC coupling mode, it is needed to add a DC bias voltage circuit BIAS-T1 to the driver and add a DC bias voltage circuit BIAS-T2 to the EAM, wherein the BIAS-T1 and BIAS-T2 are used for providing the DC bias voltage to the driver and the EAM, respectively, and are mainly composed of magnetic bead and inductor, for passing DC and blocking AC. Thus, when the driver and the EAM use the AC coupling mode, it is needed to add the DC bias voltage circuit (i.e. circuit BIAS-T2) to the EAM, so as to enable the reverse bias voltage of the EAM to fall within the range of modulation of EAM, which means that the absorption of light intensity of the EAM increases in an approximately exponential manner with increase of the reverse bias voltage.
The driver and the EAM use the AC coupling mode, which can reduce the power consumption of the driver; adding the DC bias voltage circuit to the EAM can ensure the stability of output optical power of the laser. However, the DC bias voltage circuit (BIAS-T2) in FIG. 2 is set between the driver and the EAM, and the DC bias voltage circuit in the traditional art generally includes components, such as inductor; because the used components are not ideal, the parasitic parameters are unavoidable, namely, there exist parasitic resistance and parasitic capacitance, which causes a high-frequency AC signal output by the driver to be shunted by the BIAS-T2, thereby the high-frequency AC signal to the EAM is lost; the loss causes large jitter of output optical carrier wave of the laser and small margin of eye-diagram module, which decreases high-frequency performance of the laser.